Heat engine with regenerator and timed gas exchange

ABSTRACT

A Stirling-like system incorporating a heater, a displacer and a regenerator is intermittently coupled to an external system via valves, providing pneumatic power while ridding waste heat. The external system is commonly a Rankine cycle, sharing the working fluid of the Stirling-like system, and can be used for heat pumping, distillation and drying. The Stirling working fluid and the Rankine working fluid are the same material and are exchanged between the two systems. A dual Stirling-like system mates a heat engine with a heat pump, sharing the same pressure-containment, with the dual system intermittently coupled to external environments for convective exchange of heat and cold.

U.S. Provisional Patent Application No. 61/209,921, dated 12 Mar. 2009,“Stirling engine for direct mechanical compression,” by the inventorSeale named in the present application, is incorporated here byreference. The more recent U.S. Provisional Patent Application No.61/336,494, dated 22 Jan. 2010, “Heat engine with regenerator and timedgas exchange” by inventors Seale and Bergstrom of the presentapplication, is further incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to heat engines and heat pumps,incorporating aspects of Stirling engines and engines with timed openingof valves for gas exchange, particularly diesel engines. The inventionis useful for heat pumping, refrigeration, and also for recycling ofsteam latent heat in superheated steam drying.

BACKGROUND OF THE INVENTION Earlier Referenced Work Related PastTeachings

The following Specification will teach a core invention that can beviewed from several perspectives and can be configured in a variety ofways. The invention is a heat engine and a heat pump—two “separate”terms that refer to a device and a related process that can be employedin two directions: as a heat engine to convert a “downhill” hot-to-coolflow of heat into mechanical power; and as a heat pump to convertmechanical power into an “uphill” cool-to-hot or cold-to-warm flow ofheat. The new invention will teach a merger of the heat engine and heatpump aspects into a unitary whole with the elimination of several costlyand wasteful intermediate energy conversion steps. Important backgroundfor the present invention is found in the technology of Stirling enginesand Stirling heat pump/refrigeration systems. Yet, most “Stirling”systems are closed thermodynamic cycles, where heat is conducted in andout through the walls of a hermetic containment. In some of theliterature, a “Stirling engine” is a closed hermetic system bydefinition. Thus, parts of the present invention will be described as“Stirling-like” components or subsystems, sharing characteristics incommon with Stirling engines but differing in three important respects:

-   -   1) Heat is exchanged by timed convection through valves rather        than by conduction into and out of a hermetically closed system.    -   2) Adiabatic processes are substituted for parts of the        “classic” Stirling cycle that called for continuous heat        exchange between the internal system and external heat source        and sink reservoirs.    -   3) Pneumatic pressure-times-volume energy exchanges are employed        directly without the intervention of power pistons.

Pertinent to the present invention are examples of so-calledStirling-Diesel hybrids: systems that include valves and gas exchangewith the external system or environment, operated in conjunction withreciprocating gas flow through a regenerator. Patton, in U.S. Pat. Nos.7,219,630, 7,004,115 and earlier patents, teaches a system employing twopistons, one for intake and compression and the other for power deliveryand exhaust functions, the first piston being coupled to the secondthrough a regenerator. A parallel is seen where the core components of aStirling engine are a displacer piston, a regenerator, and a powerpiston. Unlike external-combustion, hermetic Stirling engines, Patton'ssystem resembles a Diesel engine, in that it breathes air and employsdirect fuel injection into a gas that is sufficiently hot to causeimmediate combustion without spark ignition. While diesel enginesachieve the high air temperatures required for combustion through highcompression ratios (typically 18-to-1) and the accompanying adiabaticheating, Patton's system uses low compression while most of the neededair pre-heating is accomplished with a regenerator. Timed internalcombustion heat is produced, by fuel injection, in the “rightplace”—inside the combustion chamber, as opposed to externally—at the“right time”—when the power piston is being driven down, early in apower stroke. Heat that conducts inward through the walls of aconventional Stirling cylinder flows at all times. Idealized diagramsmay show the path of incoming heat “blocked” by a moving regenerator orone or two moving pistons, but in such a situation, heat continues toflow into the sides of the regenerator, so there is little effective“timing” of the heat flow. Indeed, there is a tendency for a maximumheat flow rate to occur in a Stirling cylinder at the “wrong time”—whenthe cylinder temperature is at a minimum and the power piston isperforming a compression stroke.

Patton provides an excellent review of the prior art, including manyreferences giving relevant background to his own and the presentinventors' teachings. In one such reference, U.S. Pat. No. 5,050,570,Thring teaches an “Open cycle internal combustion Stirling engine”incorporating two pistons with coaxial shafts and sharing a commoncylinder, a typical Stirling engine configuration, also including aregenerator, but equipped with timed valves, fuel and spark ignition. Inthe more recent U.S. Pat. No. 5,499,605, Thring teaches a two-pistonStirling-hybrid configuration that anticipates the more advanced recentwork of Patton. As will be seen, however, the present invention offersmany useful, energy-saving functions not anticipated in Patton's work orthe earlier work of Thring and others. In U.S. Pat. No. 5,632,255,“Regenerated engine with an improved heating stroke,” Ferrenberg teachesthe use of a single moving element combining the functions of aregenerator and a displacer piston, henceforth described as a“regenerator piston” in the Specification below. Ferrenberg shows that apower piston and regenerator piston sharing a common cylinder canperform functions requiring two separate cylinders where the regeneratoris a fixed component with through-flow of gas driven by a separatedisplacer piston. While Ferrenberg claims certain performance advantagesto this unitary cylinder approach, more recent teachings of Patton(e.g., U.S. Pat. No. 7,219,630) show five valves used in conjunctionwith separate compressor and power pistons to accomplish a highlyefficient hybrid Stirling-Diesel cycle. In U.S. Pat. No. 6,457,309,“Multifuel internal combustion Stirling engine,” Firey teaches pistonswith coaxial shafts sharing a common cylinder, which he calls “displacerpiston” and “compression piston.” Similar language is echoed in theSpecification below, except that in place of “compression piston” theterm “power piston” is used generically to describe both pistons thatconvert shaft power into compression power for refrigeration, and thatconvert pneumatic power to shaft power in heat engine. operation. Powerpistons generally require sliding seals to fulfill pressure-bearingfunctions, though systems demonstrated, for example, by Global Coolingof Athens, Ohio, achieve power piston functionality with air bearingsand no sliding seals. As will be seen in the following Specification,important functions traditionally requiring power pistons can beaccomplished by purely pneumatic means, without the intervention ofsolid power piston components, nor of water pistons and the like (astaught for example in U.S. Pat. No. 4,676,066 by Tailer et. al., and inmore recent teachings that reference Tailer.). Unlike a Stirling powerpiston, a Stirling displacer piston does not require tight slidingseals, but rather only a moderately close fit in the cylinder, since thelow flow resistance of a typical Stirling regenerator results in littlepressure difference across a displacer piston. Firey teaches aconfiguration wherein the displacer piston operates between thecompression (or “power”) piston and the region where cylinder walls areexposed to hot combustion products. It is highly desirable for acompression or power piston to operate in a relatively cool cylinder, asthis minimizes thermal expansion problems, reduces wear and results in asystem that tolerates contamination and grit, including from combustionof dirty fuels (including coal in Firey's example.) This advantageousprotection of heat-sensitive components by a displacer piston is carriedinto new and unanticipated contexts in the invention to be describedbelow.

Stirling refrigeration systems are well known in the art, and have foundparticular application for cryogenic operation. In U.S. Pat. No.4,996,841, Meijer et. al. teach a “Stirling cycle heat pump for heatingand/or cooling systems” wherein a Stirling engine directly powers therotary shaft that drives a Stirling heat pump. This extreme proximity ofthe fuel-powered prime mover to a heat pump might be contrasted with theSolar One and Solar Two projects by Stirling Energy Systems inCalifornia's Imperial Valley and Mojave Desert. There, solar-poweredStirling-electric generators are projected to produce over 1000 peakmegawatts of electricity, whose greatest value to the utility system isto meet correlated extreme air conditioning load demands. While Meijeret. al. reduce the gap between Stirling producer and heat-pumping userfrom hundreds of kilometers to a fraction of a meter, it will be seenthat the present invention brings these functions still closer together,in a manner that is compatible with solar power and that, solar- orfuel-driven, eliminates costly and wasteful intermediate energyconversions.

A rapidly emerging technology for drying of wet solids, ranging fromgrains to wood chips to sewage sludge, conducts the drying process insuperheated steam, whose mass is increased as the drying wet materialsgive off steam. This continuously-produced steam is collected,compressed, and forced to condense at a temperature above the boilingpoint associated with the steam pressure inside the drying apparatus.The resulting steam condensation heat is transferred back into thedrying apparatus, effectively recycling this heat energy to promotefurther drying. The Swedish company G.E.A. Barr-Rosin has successfullyimplemented this technique in multiple industrial applications,typically drying in a sealed apparatus at several atmospheres' pressure,while others have demonstrated similar techniques at lower pressures andassociated boiling temperatures for use with heat-sensitive materials.These energy-saving processes are powered by a costly form ofenergy—electricity. As will be seen, the current invention extendsnaturally, in its applications, into the area of efficient drying, wheresuperheated steam becomes the working fluid of an open-cycleStirling-like system that interacts very directly with the dryingmaterials. Recognizing that steam from drying materials will commonly beladen with grit, whether from laundry of sawdust being dried forfuel-wood pellet production, and recognizing that thorough filtration ofgrit from large volumes of steam entails costs and technical challenges,it will be appreciated that Meijer et. al. teach ways to make a Stirlingengine that is tolerant of grit. The connection being suggested here wasnot recognized by Meijer et. al., however, nor by the growing industriesthat perform superheated steam drying. Effective energy-saving andcost-saving hybrid technologies of this sort are much needed, with anumber of examples being taught below.

Pertinent Heat Engine Principles

The invention to be taught below is best understood from a background ofheat engine principles that have been applied, in separate contexts, toStirling and Diesel engines. These engines are understood in a broadgeneralized context from the perspective of their associated idealizedthermodynamic cycles. Though these cycles are amply described in theliterature, the terminology and approaches differ from place to place.To establish background with a consistent approach and vocabulary theidealized Stirling and Diesel cycles will be reviewed briefly here,along with the Carnot cycle, which provides an instructive ifimpractical example of the best performance that can theoretically beachieved with a heat engine. The Specification will then proceeddirectly from these known thermal cycles to new cycles and variations,shown first as abstract graphs and then in exemplary practicalembodiments of the invention.

The fundamental benchmark for heat engine efficiency was described byCarnot, in the form of equations and graphs relating to the idealizedcycle bearing his name. The diagrams of FIGS. 1 a and 1 b are labeled“Prior Art” since they show concepts that have been known since the1800s, though the particular illustrative forms, by an author of thispatent, may be original and are chosen to demonstrate a conceptualsymmetry that will be embodied in a practical invention, as taught inthe following Specification.

In diagram 100 of FIG. 1 a, the left side represents operation of a heatengine, converting a spontaneous, downhill (i.e. hot-to-cool) flow ofheat to mechanical energy as work, while the right side representssymmetric operation as a heat pump, converting mechanical energy or workinto a driven, uphill (i.e. cool-to-hot) flow of heat. In thismathematical idealization, approachable but not achievable in real-worlddevices, the energy transformations are reversible, as understood inthermodynamics. This implies that the total entropy of the system plusenvironment is unchanged throughout the process, whereas the non-idealbehavior of real systems inevitably causes an increase in entropy. Givenan entropy “S”, an infinitesimal change in entropy of an object, “dS” isgiven by the well known equation:

dS=dQ/T

Here, dQ is an infinitesimal quantity of heat energy “Q” flowing intothe object, and “T” is the absolute temperature, described in thisSpecification in Kelvin units, though Rankine units are also applicable.If an infinitesimal quantity “dQ” of heat flows from a first object attemperature T1 through a thermal flow resistance and into a secondobject at a lower temperature T2, then the change in entropy of thefirst object is dS1=−dQ/T1, a decrease since the object loses heat,while the change in entropy of the second object is dS2=dQ/T2, anincrease of greater magnitude than “″dS1|” (read: “absolute value ofdS1”) since denominator “T2” is smaller than denominator “T1”. Thus, thesum “dS1+dS2” is seen to increase whenever there is a temperature dropdue to thermal flow resistance. If two objects are in thermalequilibrium at equal temperatures, then there will be no flow of heat.The observation that heat always flows “downhill” from higher to lowertemperature, or does not flow at all for systems at equal temperatures,is re-stated in thermodynamics as a postulate, which along with verylittle additional information leads to the derivation of the Second Law(of Thermodynamics), namely that the entropy of a closed system alwaysincreases or remains the same. In that context, FIG. 1 and severalidealized figures to follow represent thermodynamic behavior in themathematical limit of approach to equilibrium, where heat flow ratesapproach zero along with the temperature differentials associated withheat flow and thermal resistance. These idealizations representconceptually useful optimum limits for performance, while theengineering task to follow is to seek real systems whose efficienciesare a reasonably large fraction of the “Carnot Ideal” as now describedin diagram 100 and in some figures to follow.

In 100, a large heat reservoir 102 is at a high temperature, for example900 Kelvins, as labeled. Heat flows reversibly (i.e. with no temperaturedifferential and no increase in entropy) via 106 into a heat engine 108,represented schematically by a vertically elongated rectangle. The dotpatterns in his rectangle and the square blocks representing heatreservoirs indicate temperature by analogy to density of atoms ormolecules of an ideal gas at a given constant pressure. Thus, astemperature approaches zero Kelvins, the gas particles come very closetogether and the dot density approaches black, while at hightemperatures the gas density and dot density are low. Thetemperature-indicating dot density in 108 represents the operatingtemperature range from zero to the maximum temperature of the system,here 900 Kelvins by way of example. Heat engines require a heat sourceand a heat sink, and in this case the heat sink is represented bythermal reservoir 118, whose dot density is higher than in 102 torepresent a lower temperature, 300 Kelvins in this example. Heat flowsinto 118 via path 116. The vertical extent of the curly bracketsrepresent temperatures or temperature ranges: here the high temperatureof 102 by bracket 104, the lower temperature of 118 by bracket 112, andthe temperature difference between 102 and 118 by bracket 110. In heatengine 108, heat flows downhill across the temperature difference 110,which in this example is two-thirds as great at the absolute temperatureindicated by bracket 104. In flowing two-thirds of the distance from themaximum system temperature toward absolute zero, two-thirds of the heatenergy flowing through 106 is converted to a mechanical energy output114, while the remaining one-third of the heat energy is not recoverableas mechanical energy and dumps into the heat sink 118 via 116. Thegeneralization is easily seen. The maximum fraction of heat energy thatcan be converted to mechanical energy or work in a heat engine is thesource-to-sink temperature differential (110) divided by the absolutetemperature (104) of the source. This is expressed by the famous Carnotequation.

The fact that the process on the left of 100 is reversible implies boththat there is no entropy increase and that the process can in fact berun in reverse, as the heat pump represented on the right of 100. Here,mechanical energy flows via 114 into heat engine 128, here operating asa heat pump, which uses its mechanical input energy to draw heat from areservoir 122 at temperature 124 via path 126 into the engine. In thisexample, the output temperature is represented by 130, which isidentical to 104, while the difference between 130 and 124 is theequivalent temperature difference 120. The quantity of output heatenergy from 128 via 132 into thermal reservoir 134, at temperature 130,is seen to be the sum of heat energies entering the heat pump via paths114 and 126, with the ratio of these two energy flows being representedby the ratio of height 120 to height 124. In the illustrated case,two-thirds of the output heat flow comes from mechanical energy flowingvia 114, while the remaining one-third comes from heat energy drawn from122 via 126. The ratio “two-thirds” is the same for the heat pump as itwas as described above for the heat engine in this example, where thetemperatures on the two sides match. It is not, however, necessary thatthe temperatures on the two sides match. Mechanical energy flowing via114 is a “general purpose” type of energy whose use varies with context,as seen in FIG. 1 b.

In diagram 150 of FIG. 1 b, the system 152 on the left represents thesystem on the left of diagram 100, here shrunk graphically in thevertical dimension to illustrate a new situation. The rate of heat flowalong path 156 from system 152 is considered to be the same as the flowalong path 114 of diagram 100. On the right side, however, the maximumtemperature 174 is much lower, 320 Kelvins in this example, while heatflows out of source 160 at temperature 164, 270 Kelvins in this example,via path 162 into heat pump 168. It is seen graphically and numericallythat the source temperature and sink temperature are separated by asmall fraction of the absolute temperature of the sink, and this impliesa high Coefficient of Performance, or CoP, of the heat pump: the ratioof output heat flow via 170 to input mechanical energy flow via 156 islarge. Furthermore, looking at the heat engine on the left side, wherethe heat source is much hotter than the heat sink, a large fraction ofthe source-derived heat energy flows out via 156 to the heat pump.Clearly, the conditions that yield high efficiency for a heat engineyield low efficiency for a heat pump, and vice versa.

As will be taught in the following Specification, it is possible toconstruct a highly efficient heat-powered heat pump employing ahigh-temperature heat source such as 102 (of 100) providing a small heatflow 106, so that a large heat flow is drawn across a relatively lowtemperature differential 158, drawing heat 162 from, and possiblyrefrigerating or air-conditioning, a heat source 160, while delivering“waste” or “useful” heat 170, and thereby heating a heat sink 172. Thetemperature 112 of heat sink 118 in 100 is shown as intermediate betweenthe source and sink temperatures of system 150. In a system combining aheat engine and a heat pump to make a heat-powered heat pump, the heatsink 118 for the heat engine 100 becomes heat sink 172 of diagram 150.The high temperature heat sink 134 of diagram 100 becomes the lowertemperature heat sink 172 of diagram 150, while the heat engine heatsink 118 of 100 is effectively combined with the heat pump heat sink tobecome the overall heat sink 172. By analogy, one can think of anelectrical transformer with two terminals on the primary or power inputside and two additional terminals on the secondary or power output side,a four-wire device. If one primary terminal is interconnected with onesecondary terminal to a common ground, then one has a three-terminaldevice, or similarly, a three-wire autotransformer. The thermal systemof diagram 150 abstractly describes a three-terminal thermal “step downautotransformer.” Employing analogous electrical terminology, one has a“high voltage” or high-temperature source for the heat engine component152, not numbered separately but analogous to source 102 of diagram 100,a secondary “ground potential” or low-temperature source 160, and the“autotransformer” output terminal as heat sink 172, which receives both“waste” heat from system 152 and pumped heat from source 160. Where theintention is heating, whether for drying, space heating, distillation,or similar functions, the “waste” heat is not wasted but is part of theuseful system output, combining with the pumped heat to achieve aneffective system gain or Coefficient of Performance, “CoP”. In commonusage, however, “CoP” refers to gain from electrical wattage input tothermal wattage output. In diagram 150, the system “CoP” is fromhigh-temperature thermal power input to lower-temperature thermal poweroutput.

Diagram 150 represents a theoretical possibility, not a practicalimplementation. As will be shown, there are means and methods forachieving usefully large fractions of the ideal heat-to-heat CoPperformance or “Thermal Leverage” implied by these diagrams and theunderlying Carnot equations for converting heat to work and work back toheat.

The Stirling Engine was first described by a Scotsman, the Reverend Dr.Robert Stirling, in an 1816 patent, and demonstrated in 1818, where itwas used to pump water. The term “Stirling engine” has come to refer toa class of heat engines that incorporate an external heat source, a heatsink, and an internal gas cycle for producing mechanical energy. Theterm “Stirling heat pump” has come to refer to devices similar toStirling engines but configured to operate in the opposite direction,employing mechanical energy to transport heat from a cooler region to awarmer region, the purpose being to refrigerate the cooler region, orheat the warmer region, or both. “Stirling cycle” refers to an idealizedthermodynamic cycle that corresponds very roughly to the operation of aStirling engine or Stirling heat pump. Similarly, “Diesel cycle” is amathematical idealization of a lossless diesel engine, while “Carnotcycle” is a mathematical construct, representing a hypothetical enginethat achieves an efficiency level that can be approached but neverreached or exceeded with a real-world heat engine. These idealizedcycles, known in the prior art, are reviewed briefly here, leading up totwo new, non-conventional cycles that roughly characterize modes ofoperation of the present invention.

Graph 200 of FIG. 2 a illustrates the idealized Carnot Pressure-Volumeor P-V cycle, with pressure plotted on vertical axis 202 against volumeon horizontal axis 204. The axis units are arbitrary and chosen only forqualitative illustration. The Carnot cycle starts at the temperature ofa low temperature reservoir, following which the gas is compressedisothermally along path 206, with the gas losing heat to the lowtemperature reservoir with perfect conduction and infinitesimaltemperature drop. At the end of this initial compression, the gas isthermally isolated and further compressed, adiabatically, along path208, with the pressure rising more steeply as volume decreases due to atemperature rise to the level of the high temperature reservoir. The gasis then expanded in isothermal contact with the reservoir along path 210and finally expanded adiabatically along path 212, returning to thestarting point. It will be seen that for a real heat engine to approachthis ideal, it would have to operate slowly to approach the requiredthermal equilibrium conditions. Energy is delivered during the expansionstroke as the integral of pressure times incremental volume, the “P dV”integral under the curve. However, most of the recovered energy must beput back in during compression. The relative proximity of the upper andlower curves indicates a low Mean Effective Pressure, or MEP, anindication that, in a real engine, implies a large fractional efficiencylosses arising from relatively small frictional losses. In short, this“ideal” cycle is ideal only in a narrow mathematical sense.

Graph 250 of FIG. 2 b illustrates an idealized Stirling P-V cycle, withpressure and volume axes 252 and 254. The much larger relative spacingbetween the upper and lower curves indicates a higher MEP and a morerobust and practical system, at least in this one respect. As areminder, light smooth curve 264 inside the idealized Stirling looprepresents typical performance of a real Stirling engine. The idealizedcycle starts with isothermal compression stroke 256, similar to theCarnot stroke 206. Along 258, the working fluid, a gas, is heated bypassage through the temperature gradient of an ideal regenerator. Thissimple vertical curve hides an unreality, seemingly implying that allthe gas is heated at once while the pressure rises smoothly. If gas weresimply pushed through a regenerator, even a mathematically idealregenerator, the pressure rise would tend to heat the gas on both sidesof the regenerator, so that the ideal of perfect thermal equilibriumbetween the gas and the parts of the regenerator would be violated. Tomake this cycle ideal, it is necessary to maintain the gases on bothsides of the regenerator in perfect thermal equilibrium with theirrespective hot and cold thermal reservoirs during the regeneratortransition. This ideal is difficult to approach in practice, both forthe heating stroke 258 and the later cooling stroke 262. Following theheating stroke there is an isothermal expansion along 260 at thetemperature of the hot thermal reservoir, followed by the regeneratorcooling stroke 262, returning the system to its original state.

Observe that adiabatic expansions and compressions can, and indeed must,proceed quickly in real machines (so that there is little time for heattransfer), whereas isothermal strokes must proceed relatively slowly tominimize losses. Thus we find a shortcoming of Stirling engines. Theirdependence on equilibrium heat transfer in each of the four steps means,in practice, that it is difficult to construct a Stirling engine thatexhibits high specific power, that is, high power-per-weight or highpower-per-volume of the machine.

Graph 300 of FIG. 3 a illustrates the P-V curve of an idealized Dieselcycle, with pressure axis 302 here indicating a possible range of realpressures in atmospheres while volume axis 304 indicates a compressionratio of 18-to-1 along adiabatic compression curve 306. Dieselcombustion adds heat at constant pressure and increasing temperaturealong 308, followed by adiabatic expansion along 310. Remaining pressureabove one atmosphere is dumped through the exhaust port along 312. Theidealized closed thermodynamic cycle calls for a return to the originalstate of pressure and volume, while simply exhausting the excesspressure in still-hot gas along curve 312 would leave the cylinder withless than the original charge of gas mass, while the temperature wouldbe elevated. In practice, an exhaust stroke replaces thecombustion-heated gases with fresh cool gas, restoring the “original”state but with different gas on each stroke. Observe again the narrowcurve with the relatively low Mean Effective Pressure or MEP. The highcompression volume ratio and even higher pressure ratio imply very highpeak forces, requiring robust heavy construction.

Graph 350 of FIG. 3 b illustrates the Otto cycle, the model for a sparkignition engine, with pressure and volume axes 352 and 354 indicatingrealistic pressures in atmospheres and a realistic 8-to-1 compressionratio. Adiabatic compression 356 is followed by a constant-volumepressure spike 358 at ignition, followed by an adiabatic expansion 360.Segment 362, like Diesel segment 312, covers the actual processes ofexhaust and intake of fresh air.

Graph 400 of FIG. 4 is the last of the “prior art” cycles, indicatingqualitatively the operation of a Stirling-Diesel hybrid engine. Here thecompression ratio is quite low, with a peak pressure under 3.5atmospheres for a naturally aspirated engine. The cycle starts at oneatmosphere (read on axis 402) and one unit volume (on axis 404) andproceeds through a small adiabatic compression along 406, followed by aconstant volume heating stroke of the regenerator along 408. A trueStirling cycle would begin with an isothermal compression, while thereal-world Stirling-Diesel, incorporating “Stirling-like” aspects,employs the much quicker adiabatic compression process. The constantpressure Diesel expansion, with smooth fuel injection and combustion,proceeds along 410, followed by an adiabatic expansion power strokealong 412. The regenerator recoups waste heat along cooling path 414. Inpractice, there is still waste heat left in the engine, and even anoverexpansion may not have returned the pressure to one atmosphere.Arrows 416, back to the starting volume, and arrow 418, going all theway to zero volume, indicate a complete exhaust stroke, while arrow 420represents the intake stroke, bringing in fresh air and restoring thesystem to its original state, but with a new charge of gas.

Pure Stirling engines as well as Stirling hybrid and Stirling-likeengine designs revolve around a critical pair of components: aregenerator and either a displacer piston or a regenerator piston, thelatter combining displacement and regeneration functions in a singlemoving part. This component pair will be called a Stirling Subsystemthroughout the following Specification. A Stirling engine generallyconsists of this Stirling Subsystem plus a paired heat source and heatsink with a temperature differential to thermally power the system, plusa power piston and further mechanical energy conversion means, typicallyincluding a crankshaft, driven by the power piston. A Stirling heat pumpis fundamentally similar to a Stirling engine except that it isconfigured to work in the opposite direction, using mechanical inputenergy from a power piston to move heat “uphill” against an opposingtemperature gradient, from a heat source to a warmer heat sink. Theobjective may be to refrigerate the heat source or to warm the heatsink. As with a Stirling engine, a Stirling heat pump includes aStirling Subsystem as described. More complicated Stirling systems mayinclude multiple Stirling Subsystems, power pistons, heat sources andsinks, and interacting pistons may sometimes combine the functions ofpower piston and displacer piston in single moving parts.

The invention to be taught below employs a Stirling Subsystem as definedabove, but differs from a Stirling engine or Stirling heat pump in otherimportant respects. An understanding of existing Stirling engines isimportant for understanding the present invention.

Focusing first on the regenerator of a Stirling Subsystem, it consistsof a porous, solid, heat-resistant medium that maintains a temperaturegradient and transfers heat into and out of a gas-phase working fluid.Physically, a regenerator can be a canister of fine gravel, or afused-together mesh of crossing wires, on a ceramic honeycomb of smallgas-carrying channels, or a pressed-together bundle of capillary tubes.In an efficient utilization, gas going through the regenerator is alwaysclose to thermal equilibrium with the solid material. In normaloperation, the regenerator has a “hot” end and a “cool” end, where “hot”and “cool” are relative terms and both could be above boiling or belowfreezing. The “axial” direction of the regenerator is taken to be thedirection of the cool-to-hot temperature gradient, and also thedirection of reversing gas flow. The hot-end absolute temperature may bemore than double the cool-end absolute temperature, as a result of whichthe gas properties of density, viscosity, and molar specific heat maychange considerably from one end to the other. Ignoring these nonlinearaspects and speaking in approximate terms regarding average gasproperties, one can attribute an approximate time constant to thethermal equilibration of gas in the regenerator pores or channels withthe solid surfaces in contact with the gas. The degree of thermalequilibration of gas with the solid regenerator material can then beexpressed in terms of the equilibration time constant and the averagetransit time for gas traveling from one end to the other. Thus, forexample, if the equilibration time constant is about one millisecond andthe end-to-end transit time is about ten milliseconds, then thetemperature of gas emerging from (say) the hot end will be cooler thanthe hot-end surface by roughly 10% of the total end-to-end temperaturedifference. In that case, one could say that the gas thermalequilibration is about 90% efficient. If the gas flow rate is thendoubled, the equilibration efficiency will drop to about 80%, and if theflow rate is halved, then the equilibration efficiency will rise toabout 95%. While these characterizations are approximate in ignoringnonlinear properties, they are nevertheless useful in describingregenerator performance.

OBJECTS OF THE INVENTION

It is an object of the present invention to use a Stirling-like system,employing components typically associated with Stirling enginesincluding a heater, a displacer, a regenerator and a pressurecontainment space that allows the heater, displacer and regenerator todevelop pressure changes, but to couple these components intermittently,via valves, to an external system that receives pneumatic power from theStirling-like system via a direct exchange of working fluid with theStirling-like system. It is a related object that the valves operate sothat the pneumatic power causes a one-directional flow of working fluidin the external system, so that the Stirling-like system and valvesfunction together as a heat-powered compressor. It is a still furtherobject that this compressor be employed to drive a Rankine Cycle, forexample for pumping heat or distilling liquids or drying solids.

It is an object of the present invention to use a Stirling-like system,employing components typically associated with Stirling enginesincluding a heater, a first displacer, a first regenerator, and apressure containment space allowing the heater, first displacer andfirst regenerator to develop oscillatory pressure changes, and to couplethis oscillatory pressure to a second Stirling-like system, employing asecond displacer and second regenerator, the second displacer beingoperated in coordination with the phase of the first displacer so thatthe second Stirling-like system pumps heat. It is a related object toprovide intermittent valved coupling between the second Stirling-likesystem and separate parts of an external environment, such that workingfluid is drawn from part of that external environment into the secondStirling like system, heat is pumped from a cooled part of that workingfluid to a heated part of that working fluid inside the second Stirlinglike system, waste heat is further added to the heated part of thatworking fluid, and the cooled and heated parts of the working fluid arereturned to parts of the external environment for heating and cooling.

These and other objects will become clear from the Specification tofollow.

LIST OF FIGURES

The figures through FIG. 4 describe teachings of the Prior Art.

FIG. 1 a is a graphic representation of the algebraic equations ofCarnot describing the efficiency of an ideal heat engine and an idealheat pump, with graphic emphasis on the symmetry of the heat engine andheat pump efficiencies.

FIG. 1 b is a variation on FIG. 1 a where the heat engine drives theheat pump, but the temperature differences are not symmetric, with theresult that a large Coefficient of Performance can be achieved.

FIG. 2 a is a pressure-volume diagram of an ideal Carnot cycle.

FIG. 2 b is a pressure-volume diagram of an ideal Stirling cycle, with asuperimposed curve representing non-ideal performance of a real Stirlingengine.

FIG. 3 a is a pressure-volume diagram of an ideal Diesel cycle.

FIG. 3 b is a pressure-volume diagram of an ideal Otto cycle.

FIG. 4 is a pressure-volume diagram of a hybrid Stirling-Diesel cycle.

FIG. 5 is a pressure-volume diagram for an idealized cycle of thepresent invention for using a Stirling-like engine to compress workingfluid through check valves from a low pressure region to a higherpressure region.

FIG. 6 is a pressure-volume diagram for an idealized cycle of thepresent invention for using a Stirling-like engine pneumatically coupledto drive a Stirling-like heat pump.

FIG. 7 a illustrates components of a Stirling-like system, including aheater and a Stirling subsystem.

FIG. 7 b provides a second perspective view of the regenerator of FIG. 7a.

FIG. 8 shows a Stirling-like system coupled via one-way check valves toa distillation system.

FIG. 9 shows details of the distillation system of FIG. 8.

FIG. 10 shows a two-stage Stirling compressor driving a Rankine-cycleheat pump.

FIG. 11 shows a Stirling compressor used in a superheated steam dryingsystem to dry lumber with recycling of condensation heat.

FIG. 12 shows a Stirling subsystem with output check valves and inputheat from a concentrating solar collector.

FIG. 13 shows a Stirling subsystem with heat input from a flame.

FIG. 14 shows a more efficient way to transfer the flame heat of FIG. 13into the working fluid of the Stirling subsystem.

FIG. 15 shows a hybrid Stirling-Diesel engine with an electricmotor/generator to start the displacer piston and then be driven byStirling action, while inlet and outlet check valve transfer pneumaticpower to an external load while providing convective removal of wasteheat.

FIG. 16 shows a Stirling-like engine that outputs pneumatic power viacheck valves and inputs heated gas for convective input of heat to drivethe system.

FIG. 17 shows a dual-Stirling engine with two regenerator pistons, forheat-powered heat pumping between gaseous working fluids within thesystem, and with timed exchange of those working fluids with an externalenvironment.

FIG. 18 is a timing diagram showing positions as functions of time forthe two regenerator pistons of FIG. 17.

FIG. 19 shows an elaboration of the system of FIG. 17 incorporating theconvective heat input of FIG. 16.

FIG. 20 is a timing diagram for FIG. 19 analogous to the timing diagramof FIG. 18 for FIG. 17.

FIG. 21 shows a dual-Stirling engine functionally similar to that ofFIG. 17 but employing two displacer pistons and two fixed regenerators.

FIG. 22 a through 22 q are small iconic diagrams of the dual-Stirlingengine of FIG. 21, showing the coordinated piston motions, valveopenings and closings, and working fluid flows of that engine.

SUMMARY OF THE INVENTION Preliminary Concepts

The summary begins with a brief continuation of the abstract idealcycles discussed previously. In graph 500 of FIG. 5, again plottingpressure 502 against volume 504, we view the essential operation of aStirling Compressor. The cycle begins with no mechanical compression,but simply regenerator heating at constant volume along 506, raising thepressure, for example, from one to two atmospheres with a doubling ofabsolute temperature. Regenerator heating continues as an outlet valveopens to a large gas reservoir at the high pressure, e.g. twoatmospheres, and expansion volume is displaced along segment 508 atconstant pressure. A short vertical line indicates transition to heataddition, for example by combustion in a Stirling-Diesel hybridcompressor, and volume expansion continues along the line 510 withcircular bumps. The outlet valve closes and a return regenerator strokelowers the pressure along 512. Then, as with the other valved cycles, wehave an exhaust stroke along 514 and 516 and an intake stroke along 518.These strokes could in principle be omitted, except that then therewould be less cooling gas exchange, reducing the effectiveness of theregenerator. Tradeoffs for simplicity often entail compromises inefficiency. If the outcome, with efficiency compromises, makes itpractical and inexpensive to conserve energy that previously was totallywasted, then the overall approach may be worthwhile. As will be shown inthis invention, systems that are “inefficient” in some respects canstill provide large fractional reductions in energy consumption inneglected areas of heat pumping and heat recycling at low temperaturedifferentials.

In graph 600 of FIG. 6, the pressure-volume is tilted “backward.” Wehave gone from large compression strokes in graphs 300 and 350 to asmall compression stroke in 400, to no compression prior to heating in500, and graph 600 we move “beyond no compression,” with moderateefficiency compromises and accompanying great rewards through reductionof previously serious performance and economic losses. Regeneratorheating stroke 606 at constant volume is followed by expansion with acombination of regenerator action and heating from a heat source alongrising pressure curve 608. Volume axis 604 indicates a low compressionratio while pressure axis 602 indicates low pressure change. Here, theworking fluid, a gas, in the core Stirling-like heat engine is expandingagainst a second gas volume, which is being compressed and which offersincreasing resistance to that compression, thus causing the “unexpected”rise of pressure with expansion of the graphed “primary” volume. Thereis a regenerator cooling stroke along 610 and then decreasing pressurewith compression and gas release as the interacting “external” loadpressure falls along 612. Exhaust and intake strokes along 614 and 616rid the system of waste heat in preparation for another power cycle.This graph provides a crude indication of operation of adual-Stirling-like cycle in which a Stirling-like heat enginepneumatically powers a Stirling-like heat pump.

The term “Stirling-like” is used throughout this Specification todescribe thermodynamic cycles that employ a regenerator to captureuseable heat energy, develop pressure change, and perform pneumatic workagainst a load. In related usage, the present invention provides fordirect pneumatic power production and pneumatic power-to-pumped-heatconversion through novel uses of the “Stirling Subsystem” as describedin the above “Background . . . ” section as “ . . . a regenerator andeither a displacer piston or a regenerator piston, the latter combiningdisplacement and regeneration functions in a single moving part.” Tocomplete a heat engine or heat pump, one needs at least two heatreservoirs, either drawn upon collectively as a source of power in aheat engine, or heat-pumped from the lower to the higher temperaturereservoir in the case of a heat pump that is driven by an externalsource of mechanical input power. Diagram 150 of FIG. 1 b suggests asystem with three heat reservoirs, functioning as a thermalautotransformer and using high temperature heat more-or-less directly topower heat pumping from a low-temperature heat source to a heat sink.That output heat sink, as in sink 172 of diagram 150, which is commonlybut not necessarily intermediate in temperature between the driving heatsource and the low temperature reservoir (160) from which heat is drawn.It is recognized that a system like this can potentially pump relativelysmall quantities of heat up to a temperature higher than that of thepowering heat source, though the examples below will focus on pumpingheat to a reservoir, like 172 of diagram 150, at an intermediatetemperature between the other two terminals. The objective, then is toaccomplish heat pumping by primarily pneumatic means, with reduction orelimination of the power piston function in a system optimized forgas-flow exchange of both pneumatic and thermal energy. The convectiveexchange of thermal energy is an important component of this new system,as convective exchange goes generally much faster, in systems ofcomparable dimensions and weight, than combinedconvection-with-conduction through a pressure containment wall.Convective heat exchange and pneumatic transmission of mechanical powerare complementary functions in this new system.

Recalling the electrical transformer or autotransformer analogy, theelectrical system invented by Nicolai Tesla and deployed by Westinghouserequired alternating current “AC” electric power. The term “AC” will beused below in a generic sense to include oscillatory pneumatic power,which delivers energy in pulsatile fashion but in a one-way directionwhen pneumatic pressure and volume flow oscillate together in-phase. Asin electrical systems, “reactive power” describes a situation with nonet one-way flow of energy when pressure and volume flow-rate are inquadrature phase. Reactive pneumatic power is usually counterproductiveand to be minimized. Regarding sources of “AC” pneumatic power, timedinternal combustion is an excellent example of heat flow in pulses thatare timed to cause in-phase variation of pressure and volumedisplacement. Traditional Stirling engines suffer because it isdifficult to modulate the flow of input heat for optimal timing, but theregenerator largely overcomes this limitation. The Stirling Subsystem,including the regenerator and displacer means, is an effectivethermal-to-pneumatic DC-to-AC converter, producing an oscillatorypressure variation with flow for volume displacement. A Stirling heatpump is a pneumatic-to-thermal AC-to-DC converter. Thus, we see thebeginnings of a thermal DC-to-DC converter that employs the StirlingSubsystem as the necessary intermediary for efficient thermal energyconversion from one temperature differential to another, realizing the“promise” implied by diagram 150.

The Core Invention

With minor exceptions, embodiments of the present invention use nomechanical piston, avoiding sliding seals, connecting rods andcrankshafts and related components. The only mechanical part undergoinglarge motions is a displacer piston, which may optionally incorporate aregenerator into the moving piston itself and be called a regeneratorpiston, or which may be a non-permeable piston that drives gas through aseparate fixed regenerator. The piston, generally driven by a low-powerelectric motor, incorporating or working in conjunction with aregenerator, responds to heat from a heater to produce oscillatorypneumatic power. This power may be used in two ways.

In a first power use, the gaseous working fluid of the Stirling-likecore system may be a gas to be compressed, and compression may beaccomplished through rectification of the oscillatory pneumatic power,typically employing two valves per compressor stage. Two or moreStirling Compressors may be cascaded to handle larger ratios of loadpressure. This Stirling compression drives a Rankine cycle includingevaporation and condensation with associated uptake and release of heat.An obvious application is Rankine cycle heat pumping, using a closedrefrigerant cycle, for example as applied to space heating and airconditioning. Propane is a viable working refrigerant fluid for thispurpose, being a viable but far from ideal Stirling working fluid.Extreme high temperatures cause excessive decomposition of propane andmust be avoided. An important working fluid in the realm of Stirlingcompression is water vapor, which is not subject to high-temperaturedecomposition in typical Stirling-like applications. Applications ofwater vapor compression include superheated steam drying, distillation,and concentration of solutions, for example, of maple sap to make syrup.An already well developed field is superheated steam drying withelectrically driven compression and recovery of the heat of forcedcondensation. The new invention eliminates the electrical step and thesubsequent mechanical steps of the compression process, going straightto thermally-driven pneumatic compression, for example, of water vapor.Among many uses to be contemplated are heat-driven heat-recyclingclothes dryers, lumber kilns, apparatus for drying wood chips and otherbiofuel components, grains and other foods, and manure and sludge.Systems can be powered flexibly by fossil fuels, biofuels, andconcentrating solar collectors. The thermal-to-pneumatic energyconversion efficiency is usually moderately low, but the other side ofthe equation is often an offsetting high Coefficient of Performance orCoP in converting the pneumatic power into complementary processes ofevaporation with closely coupled condensation and heat transfer to drivefurther evaporation. The large fraction of “waste” input heat from thisprocess is mostly retained and used for evaporation and to overcomesystem heat losses. Overall heat-in to heat-out gains typically rangefrom two to five, with the figures being strongly dependent on design,application, and operating conditions.

When gas is exchanged through a Stirling compressor, heat is carried outof the system by gas convection, eliminating the usualperformance-limiting Stirling bottleneck of heat elimination byconduction out of a sealed enclosure. The intermittently-coupledexternal Rankine system becomes the extended heat sink for the StirlingCompressor. As is suggested in graphs 500 and 600 and specifically theexhaust and intake cycles of 516, 518, 614 and 616, extra convectivecooling of the Stirling subsystem, when its valves are open, providesimproved heat removal and enhanced performance. Even though atmosphericpressure steam is subjectively “hot,” it is nevertheless much coolerthan combustion temperatures, while the Stirling-related thermodynamicproperties of steam are moderately good.

In a second category of use of pulsating pneumatic power from aheat-driven Stirling subsystem, the “AC” pressure variation is exploiteddirectly, without valve rectification to a unidirectional flow.Specifically, conventional Stirling heat pumps use cyclic mechanicalcompression, in phased coordination with regenerator motion, to moveheat. Typical existing applications entail large ratios of absolutetemperature and take advantage of the high heat capacity ratio or“gamma” of helium gas. For space heating and air conditioningapplications, however, the needed ratios of absolute temperature aresmall, which relaxes the technical requirements of the system design.Air, with its slightly lower heat capacity (7/5, as opposed to 5/3 forhelium), varies less in temperature over a given volume compressionratio, but the higher specific heat of air (compared to helium) partlycompensates for the smaller temperature fluctuation. Particularly “lowlift” (i.e., low absolute temperature ratio) heat pump applications canuse a particularly simple coupled-cylinder dual-Stirling design, as willbe taught. Higher “lift” applications are performed effectively with amore integrated dual-Stirling design in which a heat engine regeneratorpiston travels in the same cylindrical space as the heat pumpregenerator, in overlapping ranges of motion so that the effective deadvolume of the system is extremely low.

Both categories of application share the same driving system, which is aStirling subsystem producing oscillatory pressure variation and thenopening valves to a cooling heat exchange environment or coupled system.

DETAILED DESCRIPTION OF EMBODIMENTS

Going through various embodiments of the invention, FIG. 7 a illustratescomponents of one example of a Stirling Subsystem 700. On the left,displacer apparatus 750 includes a housing 702 capable of confining theinternal volume of working fluid for pressure change. Further included,motor 704 employs magnet 706 and coil pair 708 in a simple embodiment,while more complicated and powerful motor examples will be shown below,which are already well known in the art. Flat spring 710, and a similarflat spring above motor 704, resonate the moving mass for efficientcyclic motion with low power input. These optional flat springs alsoprovide centered linear guidance of the piston motion, creating anoption for no-sliding contact guidance of the displacer motion.Displacer piston 712 is surrounded by a displacement chamber, portedwith two inlet/outlet pipes above, including pipe 714, and two morebelow. One or more ports optionally include gas valves, for example agate valve illustrated at 716, with actuation means assumed but notshown here. To the right of apparatus 750 is regenerator 760, includinghoneycomb holes 720 in body 718. Many regenerator configurations, bothfixed and as moving regenerator pistons, are known in the art, and it isunderstood that the coarse honeycomb mesh 720 is only illustrative,while a much finer mesh would usually be required. Other well knownregenerator approaches include ceramic foams, fused-together crossingfine wires, and pebble beds, this latter option being inexpensive butusually applicable only for fixed regenerators. FIG. 7 b shows adifferent perspective view of regenerator 760 for clarity. On the rightof FIG. 7 a, heater 770 includes a housing 722, a flame 724, and a heatexchange pipe 726, here drawn as serpentine, though a coiled pipe orother configuration could perform well.

FIG. 8 shows the components of FIG. 7 a in two-dimensional cross-sectionin a system for mechanical distillation or for concentration of asolute, for example, for the efficient evaporative concentration ofmaple sugar starting from highly dilute maple sap. The assembledStirling compressor system 850 includes components from drawing 700,including displacer apparatus 750, regenerator 760 (here shown insection, with a finer mesh, and with a housing) and heater 770. Thesecomponents are interconnected by pipes 802 from the displacer hot sideto the heater, pipe 804 from the other side of the heater to the hotside of regenerator 760, and pipe 806 completing the loop back from theregenerator cool side to the displacer apparatus. Valve assembly 860will be described below.

The valve 860 and distillation system 800 on the left of FIG. 8 areshown in greater detail in FIG. 9 with drawing 900. Pipe 902interconnects the displacer apparatus 750 (of FIG. 7) to valve assembly860, which includes an inlet pipe 904, a movable inlet valve gate 902spring-restored by a simple bent-wire spring, an outlet pipe 908, and amovable outlet valve gate 910. The insulated distillation reservoirincludes a high pressure inlet 912 to a chamber with condensationindicated by arrows 912 into water and into a thermal-conductivemechanical barrier. Vapor bubbles 916 rise from the oppositelow-pressure side of this barrier, and vapor rises directly from surfaceevaporation as indicated by arrows 918, with out-flow 920 completing thevapor circuit with heat-recycling exchange.

Drawing 1000 of FIG. 10 illustrates a two-stage Stirling Compressor,each stage being similar to the Stirling Subsystem of diagram 800, withsubsystem 850 shown on top, modified to share a heater flue with asimilar subsystem 1050 below. 1050 differs, however, in using a smallerdisplacer piston to work with a smaller, denser compressed gas volumecoming from 850. The two compressors are interconnected via twin checkvalve assemblies making up assembly This two-stage system shares acommon burner and flue with two serpentine heater pipes. Theelectromagnetic spring-resonated motive means for oscillating thedisplacer pistons are the same in the two Stirling Subsystems, while thehigher-pressure displacer piston is smaller, to displace the same massof gas as the upper piston, but at higher pressure and consequently lessvolume. Interconnection pipe 1002 includes heat-dissipating fins 1004,performing an intercooler function. The two displacers may optionally beoperated in opposite phases, as suggested by the diagram, while acounterweight below the permanent magnet (arrows) in the lower motorunit balances the system, such that there is little or no net verticalmotion of the system center-of-gravity as the two pistons oscillate inopposite phases. Electronic controls (not shown) are optionally equippedto maintain opposite phasing and a balance of oscillatory amplitudes tominimize vibration. Gas from compression stage-1 is cooled in anintercooler fin-tube pipe before further stage-2 compression, with thegas then proceeding to a Rankine cycle heat pump of conventionalconfiguration. Reviewing only key subassemblies of this familiar system1060, condenser 1006 receives forced convection from motor and fanassembly 1008, while evaporator 1010 similarly receives forcedconvection from fan 1012. Pressure gauges 1014 indicate the state of thesystem. Various valves, filters and traps complete the familiarfunction. These blowers, valves, sensors and associated valveregulators, etc., will be recognized by those familiar with RankingCycle heat pump systems. Note a reversing valve to switch between airconditioning and heating modes, all of which are powered primarily bycombustion power coming from the right-hand system. A valve 1016 in themiddle of the Rankine system allows the high and low pressure sides tobe momentarily short-circuited, as may be necessary to get theStirling-like system started or re-started. If there is too much backpressure on the Stirling Subsystem checkvalves, such that they fail toopen, then there will be no convective heat removal from theStirling-like cylinders, resulting an loss of the needed temperaturegradient across the regenerators. To avoid this latch-up situation, thepneumatic load is short-circuited to remove the excess pressure, allowthe valves to open, and cause the low-temperature side of theregenerator to be cooled by convection until the needed temperaturedifferential is re-established. One way checkvalves in the Rankinesystem (not shown), may be included to prevent energy-wasting back flowfrom the condenser to the evaporator when the relief valve is opened tostart or re-start the Stirling Compressor.

The working fluid for a Rankine Cycle space heating of this sort musthave appropriate thermodynamic properties, especially a criticaltemperature in the right range, and be environmentally acceptable. Thefluid must also withstand the highest temperatures of the StirlingSubsystem without excessive decomposition. Propane is an example from avery short list of potential working fluids. Most other refrigerantsthat might be used in the Rankine Cycle have poorer properties from theStirling Subsystem standpoint, and there are problems ofhigh-temperature decomposition. Even propane has limits beyond which anexcess of non-condensing decomposition products will degrade systemperformance—those include ethylene, methane and hydrogen, whilepropylene will be produced but will cycle to some extent with thepropane. The equilibrium concentration of the byproducts increases withtemperature, setting a practical upper limit to the hot-side temperatureof this system. A most detailed examination shows that solar-heat-drivensystems of this sort have good potential, while combustion-poweredsystems cannot take maximum advantage of the high temperatures that arereadily provided in an efficient burner. As is seen in other examples,water vapor as a Rankine Cycle working fluid is tolerant of hightemperatures and has better thermodynamic properties than propane, froma Stirling Subsystem viewpoint.

FIG. 11 suggests a broad generalization of the use of a StirlingCompressor for drying. In this example, a lumber-drying kiln 1100 isoperated at just above atmospheric pressure. The kiln is pre-heated andallowed to fill and over-fill with steam, until most of the air isdriven out through cracks and the building and nearly pure steam remainsinside. Since only a relatively small temperature rise is needed toreach a desired drying rate for lumber, without the warpage caused bytoo-fast drying, a single-stage Stirling Compressor 850 is shown in thisexample, while the Rankine Cycle space-heating heat pump systemdescribed previously is likely to require at least two compressionstages. In system 1100, once the kiln is filled with nearly pure steam,added steam from evaporation is collected, compressed, and caused tocondense in a heat exchanger 1102 that re-superheats the remaining steamin the kiln, thus powering continued evaporation with a significantfraction of recycled heat. Condensate liquid 1104 collects in the bottomof the condenser and is released controllably by valve 1106, so as notto lose the elevated vapor pressure. However, it is possible to detectaccumulation of non-condensing gas at the bottom of the condenser,inhibiting performance, and valve 1106 is occasionally opened enough toallow some vapor to escape, sufficient to carry out accumulatingnon-condensing gas. The excess heat of fuel combustion overcomesinsulation heat loss and provides a sufficient excess of un-recycledsteam to keep a slightly positive interior pressure, so that steam leaksout, instead of air leaking in and inhibiting the condensation process.

System 1200 of FIG. 12 shows that a Stirling Compressor can be poweredby a solar collector 1250, in this example, a concentrating parabolictrough collector. In a system of this sort, the working fluid (gas) ofthe Stirling Subsystem circulates directly through the solar-heatedtubing of the collector. Labeled interconnecting pipes 1202 and 1204from the collector to displacer apparatus 750 and regenerator 760 willreappear in later systems that optionally employ solar heat input.

Subsystem 1300 of FIG. 13 shows a perspective view in anticipation ofmore complicated “two-terminal” and “three terminal” thermaltransformers to be described. The electrically-driven displacer pistonoperates in a cylinder with four connecting pipes, two above and twobelow, as in displacer assembly 750 of drawing 700, while optional gatevalves like 716 are shown there. Assembly 1300 differs from 750 byincluding a heat source 824, illustrated here by a flame and typical gasburner apparatus, the flame heating a chamber 1350 that provides heat tothe components below by conduction. This subsystem also employs a movingregenerator piston 1302, thus differing from 750 with its displacerpiston. 1302 is illustrated as a coarse axial honeycomb mesh. Again, itis understood that a practical mesh would be much finer, and in fact,manufactured “honeycomb” meshes in ceramic filter components arecommonly square rather than hexagonal grids. A more sophisticated andefficient variation on the illustrated system will now be shown insection view.

Subsystem 1400 of FIG. 14 shows an example of the convoluted interfacepromised in the previous paragraph. The honeycomb regenerator mesh of1420 is viewed in cross section, much finer than the illustration of1300 but still more coarse than is likely to be used in practice. Solid“fingers” 1404 extend upward from the regenerator mesh into channels1402 that are surrounded by burner-heated gas. Viewed from above (notshown), these fingers and containing cylinders would be seen as a gridwith combustion gases flowing across and around the “forest” ofcylinders. The region of heated gas is hatched with a stairstep pattern.Note that this topology provides for some degree of timing of heattransfer. Inflow of heat is maximized as the regenerator pistonprogresses from mid-stroke to bottom-dead-center, exposing working fluidboth to the hot interior cylinder walls and also to the exterior fingersurfaces, which are reheated when the fingers are more fully inserted inthe cylinders. The regenerator piston is spring-restored by a helicalspring 1408, which is contained in a relatively large telescopingcylindrical shaft 1406. The spring ends are aligned to the center-axisand clamped (lower end not shown), allowing operation in alternatingcompression and tension. Passive poppet check valves 1410 and 1414 areillustrated at the bottom of the cylinder, with each poppet restored toa normally-closed position by flexible wires like wire 1416. Inlet checkvalve 1410 is shown open, allowing inflow 1412, as would occur whenregenerator 1420 is approaching its top position and the cool gas volumebelow 1420 approaches its maximum, causing overall gas contraction.

System 1500 of FIG. 15 illustrates a hybrid Stirling-Dieselconfiguration. A fuel injector 1502 is shown on the upper left, and asparkplug 1504 on the upper right, typically needed only to initiatecombustion until the system is pre-heated. Following pre-heat, theregenerator retains and transfers sufficient heat that fuel injects intoair and combusts on contact, in a smooth regenerated Diesel action. Openoutlet check valve 1506 is similar to closed outlet check valve 1414,while arrow 1508 represents the out-flow of gas. The regenerator pistonis spring-restored, as in system 1400, while motion is controlled by alinear magnetic motor/generator 1510 consisting of permanentradially-poled magnets 1512 (arrows) in the moving shaft and phase coils1514 in a ferromagnetic stator yoke. 1510 is used in motor mode forstarting the system but, as is now discussed, the piston can begin toself-oscillate and deliver power to 1510 acting as a generator.

Normally, power generation in a Stirling engine with one power pistonrequires a separate displacer piston moving in a different oscillatoryphase, typically with roughly a 90 degree phase difference. Thislimitation is overcome in interconnected multi-cylinder configurations,where phase-shifted interactions among cylinders give rise toself-oscillation of the combined displacer/power pistons. It normallydoes not work, however, to have a single piston with a wide piston headacting as a displacer piston or regenerator piston and also as a powerpiston. As illustrated here, the lower part of the piston assembly is athick piston shaft, whose opposite end travels into a region ofrelatively constant pressure, potentially acting as a power piston, ifthe pressure were in the correct phase. For ideal lossless regeneratoraction, pressure varies in phase with piston displacement, a “reactive”phase delivering no net power. For driving a self-oscillatingregenerator piston with a thick shaft rising from and sinking into aregion of relatively constant pressure, the pressure phase must shiftaway from reactive and toward a power phase, in-phase with velocityrather than displacement. When pneumatic power is drawn from the systemas described, however, and specifically when valves open after someinitial pressure change, allowing flow that inhibits or stops thatpressure change from continuing in the same direction, then this varietyof specific loading conditions causes the wall-penetrating “power pistonarea” to deliver power through the piston shaft to the generatingapparatus. Thus, for example, when passive check valves rectify thefluid flow into a fluid load with roughly constant back pressure, thecheck valves remain closed following the start of piston motion in agiven direction, while their delayed opening “clamps” the pressureprofile against further significant pressure increase until thedisplacer piston comes to a stop and the opened valve re-closes. Thepiston motor/generator will require electric power input untilconditions are achieved that provide an appropriate combination of loadback pressure, regenerator-produced pressure oscillation, and valveopenings following pressure change, increasing or decreasing. Withenergy storage for starting, as with a battery, a system of this typecan start from battery power, establish conditions for power generation,recharge the battery, and continue to produce surplus electric power. Infact, an appropriate adaptive level of electric power consumption mustthen be maintained, in order to prevent excess oscillation amplitude andbanging against mechanical limits. On the other hand, an appropriatekind of pressure loading of the inlet and outlet valves is required inorder for there to be any self-oscillation. There are known alternativeapproaches to preventing excess oscillation, for example the smallun-numbered end feature on the top of piston 1406 and the receivingdash-pot feature that the piston feature pushes into neartop-dead-center. Since the generator function of the motor/generator isrequired for starting and establishing regenerative piston oscillation,however, a small incremental expense brings about the advantage ofgenerating from excess piston power rather than dissipating that excess.

This hybrid Diesel-Stirling system for delivering both pneumatic andelectric power has the advantage of forced convective removal of heatvia the lower-left valve 1506, which functions as an exhaust valve,while the lower left valve, shown closed here, functions as the intakevalve. Note that there is little or no compression stroke in this cycle,depending on operation of the thick center shaft. P-V diagram 500 ofFIG. 5 included a discussion of this situation, which is less efficientthan a hybrid Stirling-Diesel cycle with moderate compression. Thelarger objective here, however, is not optimum efficiency, but moderateefficiency combined with simplicity and low cost, to go after the verylarge market for making considerably better use of heating fuel,delivering “bonus” pumped heat energy and possibly bonus electric power.

System 1600 of FIG. 16 shows a variation on system 1500 in whichpowering heat is brought into the upper part of the cylinder via 1608directly as hot gas, when the regenerator piston is nearbottom-dead-center, via valves that are opened by a linear cam 1602 atopa thin shaft 1604 extending from the center 1606 of the regeneratorpiston. A motor 1614 drives a blower 1612 that moves heated gas throughfrom above when the valves open, with gas exiting via 1610. Asillustrated, the blower consists of moderately high-speed bladesoperating and low attack angles so that the blades do not stall with thevalves close and prevent axial flow. The objective is a blower that doesnot dissipate excess energy while spinning against a stopped air flow.The heat source for this system may advantageously be the solarcollector system 1250 of diagram 1200, as suggested by the numbers 1202and 1204 on the input and output gas streams—these are the numbers ofthe solar collector connecting pipes.

System 1700 of FIG. 17 shows the promised dual-Stirling engine operatingas a heat-powered heat pump. Many of the components are familiar fromearlier illustrations. A heat source, for example from combustion (notshown) or from a solar collector (not shown) heats a heat exchangeregion 1750 similar to that previewed in subsystem 1400. Here, channels1702 receive fingers 1704 for enhanced and partly timed heat transfer.Warm gas flows in intermittently through the upper section via 1706 andout intermittently via 1708. Gas flows similarly through the lowersection inward via 1710 and outward via 1720. Blower blades 1712 andblower motor 1714 near 1706 are similar to ones shown in 1600, while asimilar motor 1716 and blades 1718 drive the lower circuit, with gasexiting intermittently via 1720. Flow is controlled by solenoid valves1722 and 1724 in the upper path and valves 1726 and 1728 in the lowerpath. There are two independently controlled regenerators, thinnerregenerator 1730 interfacing between cold and warm and thickerregenerator 1732 interfacing across the much larger temperaturedifferential between warm and hot. Axial motion of lower regeneratorpiston 1730 is controlled by a motor and rack-and-pinion assembly 1734,while motion of upper regenerator piston 1732 is controlled by a similarassembly 1736. In summary, the system includes two regenerator pistons,two blowers, and four solenoid-operated gas valves. The regeneratorpistons are driven controllably, optionally including withstop-and-start motion, by the servomotors and rack-and-pinion gears.Stepper motors have advantageous characteristics for this kind of a job,with controllable quick starts and stops and high torque.

An optional operating cycle for system 1800 is illustrated in diagram1800 of FIG. 19. Trace 1802 follows the vertical position-versus-time ofthe upper regenerator, interfacing between high temperature andintermediate temperature, while trace 1804 follows the thinner lowerregenerator similarly, operating between intermediate and lowtemperatures. The two regenerator traces go up together in time region1810, representing an upward regenerator piston motion in 1800 with aresulting cooling of the cylinder gas volume. “Up” in 1800 representshigh position in the diagram 1700 and lowered temperature. The heat-pumpregenerator trace 1804 then descends halfway in region 1820. It heatsair as it moves, while the side encountering cool air is cooled by thelowered temperature of the thermally-decompressed air. The regeneratorpiston stops midway in region 1830, while all four valves open toexchange warm air across above 1804 and cold air across below 1804. Thevalves re-close and 1804 completes its “downward” stroke in time region1840, continuing to pass through low-pressure, adiabatically cooled air.The “heat engine” regenerator then descends in a heating direction intime region 1850, raising the pressure in the system and adiabaticallyheating all the gases in the system. When the two pistons subsequentlyrise in a new repetition of 1810, the thinner “heat pump” piston ismoving in an air-cooling direction through air that is relativelywarmer, due to the average pressure increase compared to the times ofthe down-strokes in regions 1820 and 1840. The net effect is always tomove the warm side of the lower heat-pump piston throughcompression-heated air, and the cool side of that piston throughdecompression-cooled air. This is the well known action that makesconventional Stirling heat pumps perform. Conventionally, however, theheat pump regenerator responds to pressure changes driven by amechanical power piston. In the mechanical system of 1700, with thetiming method illustrated in 1800, the pressure changes are drivendirectly, pneumatically, by a Stirling heat engine, embodied in thehigh-temperature heat source and the thicker regenerator piston plus itslinear-motor actuation system and working in conjunction with the timedvalves. Pressure changes occur with the valves closed, in Stirling-likefashion. Valve-open gas exchanges then occur when the regenerators arecoming to a stop, or fully stopped, or just beginning to move.Conceptually, there is a time alternation between closed-systemStirling-like pressure change and open-system thermal exchange of gases.Cool gases go into the bottom of the system and come out colder, givingup their heat to the warmer gases above. Warm gases come across themiddle, are captured and heated by Stirling-like action, and emergehotter, carrying pumped heat plus combustion heat. Thus, the system hasa heat gain, or heating CoP, exceeding unity. The cool side of thesystem has a cooling CoP, not augmented by waste heat but neverthelessuseful for air conditioning, including direct solar-powered airconditioning.

Drawing 1900 of FIG. 19 combines the lower portion of diagram 1700 withthe direct hot gas exchange apparatus of diagram 1600. There are sixpaired inlet/outlet ports: 1201 and 1204, optionally recognized from1200 as solar collector ports for hot air; 1902 and 1904 for cold airexchange from below; and 1906 and 1908 for warm air exchange across themiddle. Rack and pinion drive and motor 1910 are similar to 1734 of1700, while similar drive 1736 of 1700 appears flipped around and overat 1912, partially covering 1910. This is a workable configuration ifthe rack for 1910 extends from the lower surface of the outer concentricshaft extending upward to the lower regenerator. Between hightemperature channels 1916 and 1918 one finds cam 1914, similar to thecenter part of cam mechanism 1602 of 1600 but in a middle position at1914.

The timing diagram for 1900 is similar to the one for 1700 with oneexception. Respective numbers 2002, 2004, 2010, 2020, 2030, 2040 and2050 correspond to numbers 1802, 1804, 1810, 1820, 1830, 1840 and 1850of the earlier diagram, while the start of the next operating cycle isdelayed by an extra time interval 2060, with both regenerator pistonsdown and the space above them filled with heated air. At this time ofmaximum gas temperature and pressure, cam 1914 opens the upper valve tothe hot air source, for example the air-circulating concentrating solarcollector, exchanging fresh heat into the system. The valves then close,isolating the system from gas in the solar collector or other hot airsource. Thus, the hot air source operates systematically atabove-ambient pressure. When the lower four valves open in time region2030, the system pressure is not far from ambient pressure and isrestored to ambient pressure by the opening of the valves. The overallaction is pump chilled air out the bottom of 1900 and warmed air out themiddle.

The system of FIG. 21 and drawing 2100 functions similarly to that ofdrawing 1900, excepting that this latter system employs two fixedregenerators and two separate moving displacer pistons. The regeneratorsare drawn like the others in diagrams here, as if they consisted ofnarrow honeycomb channels though a solid medium, while it is recognizedthat other approaches are viable, and many of them more economic, forinstance including fused crossed wires for a mechanically robust movingregenerator piston, or a pebble bed for an economic and effective fixedregenerator. It will also be recognized that various actuationapproaches apply, with the drawn rack-and-pinion approach being easy toimplement but potentially not as long lasting as, for instance, a linearmotor along the lines of 1510 or similar multiphase approaches. Thepurpose here is to provide relatively simple illustrations that bringout the underlying principles of the invention.

A potential advantage of the system embodiment of 21 is the flexibilitygained by not requiring a moving regenerator. A displacer piston can bevery lightweight, simplifying the linear actuation process. Also, lessexpensive options are available for fixed regenerators, particularlywhere weight is not an issue. As will be seen in following a descriptionof 2100, a performance issue is dead volume. The dual regeneratorpistons of 1700 and 1900 can move through overlapping ranges, exploitingall the available volume and thus enhancing performance. Working withingiven manageable high temperature limits, the system of 2100 cannotachieve as large an engine-mode pressure swing to drive theheat-pump-mode components. This limitation joins together with the lower“gamma” limitation of using diatomic air versus monatomic helium, alongwith related issues of the much higher molecular weight and molecularsize of air molecules, compared to hydrogen or helium, these unalterableissues leading to much lower thermal conductivity. A dimensionalanalysis of regenerator function shows that combined efficiency andvolume flow rate improve strongly with increasing regenerator area,while thickness is a minor issue, within limits and provided thatappropriate finer materials are available for construction of thinnerregenerators. With this consideration plus desire for a compact layout,the regenerators of 2100 are shown occupying the entire “floor space” ofthe working cylinders. This choice of shape was made independent of anyconsideration of a possible material. This layout also makes for a clearconceptual illustration, which will now be laid out verbally.

The detailed description of 2100 begins with naming and describing theessential components, by number, in functional categories. There are twomirror-image subassemblies, the cylindrical housings being joined bycentral bridging segment of pipe 2106. In addition to this center fluidinterconnection, there are two gas input/output pipes, left and right at2108 and 2110 across the top, and a single manifold pipe 2112 bridgingacross the bottom. The ends of 2112 terminate with servo valves, 2134 onthe left and connecting into a high-temperature heater, for exampleconnecting pipe 2104 of the concentrating solar collector drawn andreferenced earlier. The opposite valve 2136 on the lower right connectsto a gas source at an intermediate or warm temperature, for example fromthe cold air duct return of a home heating system. Near the left end,just inside valve 2134, the manifold pipe connects to the outside of aplenum consisting of a U-channel, circumferentially wrapped to capturean annular space that couples pneumatically into the left end of 2112.Holes 2140 punched through the walls of the cylinder allow gas to couplefrom the cylinder's left end into the annular plenum and connectingpipe. The mirror image of this structure is found on the right end ofthe cylinder with annular plenum 2154 coupled via holes 2146 to theinterior end of the cylinder while the plenum connects on the outside tothe right end of manifold pipe 2112, just inside valve 2136. The centerof this manifold pipe couples via servo valve 2138 and radial connectingpipe 2122 into the bridging segment of pipe 2106, as previouslydescribed. The interior of this system is divided into four regionswhose relative volumes vary due to the motion of displacer pistons. Hotand warm regions 2102 and 2126 are separated by moving regenerator 2118,driven by motor system 2114 and driving working fluid either throughregenerator 2156 or between the internal system and external systems,depending on valve settings. Similarly warm and cold regions 2104 and2128 are separated by moving regenerator 2120, driven by motor system2116 and driving working fluid either through regenerator 2158 orbetween the internal system and external systems, again depending onvalve settings.

The system of 2100 has five valves, among which two pairs arefunctionally joined to operate in the same way at the same time, whetherby common electrical control of mechanical connection. Thus, hot air orother hot gas originating from 1202 and 1204, the numbered endcomponents of the solar collector of drawing 1200, are controllablyisolated from or connected to the variable-volume hot interior region2102 by the simultaneous opening or closing of valves 2130 and 2134.Actuation of displacer piston 2118 by the motor and rack and pinionmechanism of 2114 causes volume 2102 to expand or contract undercontrol. With valves 2130 and 2134 open and the remaining valves closed,as drawn, the piston action causes gas exhaust from cylinder region 2102and complementary intake into cylinder region 2126 as the piston movesto the right, and the reverse as the piston moves left. Thus, slightlycooled hot air in 2102 can be almost totally exchanged for a freshcharge of hot air with a single stroke-right and stroke-left of 2118driven by 2114. This action accomplishes the same kind of externalheating gas exchange that takes place in time period 2060 of graph 2000,where in that case the gas exchange was mediate by blowers and gas flowthrough momentarily opened valves. System 2100 needs no blowers,although the continuations of passageways 1202 and 1204 toward theheating source might be brought together into a rectifying one-way checkvalve system that causes the air circulation at a more distant point, asin a solar collector tube, to always move in one direction.

When 1202 and 1204 close, then if valves 2132 and 2136 open as a pair,motion of regenerator piston 2120, powered via motor and rack and pinionmechanism 2116, can cause gas exchange between right-hand interiorregions 2104 and 2128, with piston 2120 starting either toward the leftas shown, or fully left, to maximize volume 2104, or with 2120 startingon the far right, to maximize volume 2128. Unlike the double-endedworking fluid source of 1202 and 1204, optionally representing theconnecting ends of a continuous solar collector tube, the fluid sourcesfeeding into paired and commonly actuated valves 2132 and 2136 are notsymmetric, being a cool or cold source feeding via 2132 into region 2128(here almost minimized) and a warm source feeding via 2136 into region2104 (here almost maximized). Because valves 2134 and 2136 share acommon passageway 2124 and it is generally desired to lose hightemperature heat via short-circuit to the warm fluid circuit, 2134 and2136 are opened only during separate non-overlapping time periods. Aback-and-forth stroke of piston 2120, driven by motor, rack and pinionmechanism 2116, therefore accomplishes an intake and exhaust stroke forone input, and in reverse order an exhaust and intake stroke for theother input, thereby exchanging heated warm air or chilled cool air withtheir respective sources. If there is a long connecting passageway foreither or both of these air sources, it might be advantageous optionallyto create a loop with one-way check valves to the right of valves 2132and or 2136 to cause gas circulation from separated points and minimizere-breathing of gas.

Note that the three-way symmetry of passage 2108 on the upper right,2110 on the upper left, and 2112 at the bottom center, suggest threerather than four external fluid connections might be feasible, with justone connecting line to hot source 1202, one to the warm gas, and one tothe cool gas. This doesn't quite work, at least for the operating cycleto be described below, for reasons that are illuminating of the systemfunction. To replenish hot air, it is desirable to open valves 2130 and2134, expel the slightly cooled hot gas from the system, and draw freshhot gas into a fully expanded region 2102, maximizing the quantity ofhot gas on the hot left side of the regenerator when regenerator actionresumes. However, when 2102 is full expanded, this represents theabove-atmospheric (or above ambient for the warm and cool gases beingused) condition of the heat pump, whose interior pressure should bebrought back down to a near-match with the warm and cold inputs beforethose valves are opened. If the system has only three valves, assignedto hot, warm and cool gases then one cannot open the hot valve and thewarm valve simultaneously for an exhaust-intake double stroke and stillmaintain pressure continuity with the closed-valve heat-pumping pressurecycle. Thus we see by counterexample that efficient operation calls forfour valves, the left-hand pair connecting for circulation into and outof the hot gas source at high pressure, and for circulation into and outof the warm and cool gas sources at a lower pressure, for exampleatmospheric pressure. The hot volume 2102 is therefore maximized beforeopening valves 2130 and 2134, then the displacer piston moves right todisplace gas out via 2130 and in via 2134, and finally the displacermoves back left to leave a maximum volume of hot gas in expanded region2102. The system then cycles, with all valves closed, to a low pressurecondition with piston 2118 shifted, hot volume 2102 minimized, and warmvolume 2126 maximized. Refreshing the warm and cool or cold gases canstart with displacer piston in any position, though a middle positionmay be desired for leaving equal refreshed half-volumes of warm and coldgas with each refresh stroke. Alternating between a full warm volume anda full cool or cold volume is feasible but entails worse pressuremismatches when valves are opened.

FIGS. 22 a through 22 q follow an example of the operational sequence ofthe system illustrated in FIG. 21. The rack and pinion mechanisms andpiston shafts are omitted from the small simplified diagrams, which areintended only to illustrate the steps of an optional operation sequence.The following short paragraphs are labeled 22 a through 22 i anddescribe the illustrated steps of the corresponding figures.

22 a The system starts at warm/cold ambient pressure, piston 2118 on theright, minimizing hot gas volume and pressure, with warm air filling theexpanded space 2126, and with all valves closed. Piston 2120 iscentered.

22 b Valves 2132 and 2136 open and piston 2120 travels full left,expelling cold air and drawing in warm air.

22 c Piston 2120 travels full-right, expelling warm air and drawing incold air.

22 d Piston 2120 returns to center, leaving half-volumes of refreshedwarm and cold air.

22 e Valves 2132 and 2136 close and valve 2138 opens to the channel 2122leading to central passageway 2106 between the regenerators.

22 f Piston 2156 moves full-left, heating gas via the regenerator andfilling the hot volume, thus raising the pressure.

22 g Valve 2138 closes, isolating the regenerators, and valves 2130 and2134 open, exposing the hot side to the external heat source via 1202and 1204.

22 h Piston 2118 strokes right, momentarily filling expanded space 2126with hot gas.

22 i Piston 2118 strokes back left, re-filling volume 2102 with freshhot gas.

22 j Valves 2130 and 2134 close and regenerator valve 2138 opens. Air onthe enclosed right side is now pressurized and at above-averagetemperature.

22 k Piston 2120 strokes right, expanding cold volume 2128 and drivingabove-average-temperature warm air into the warmer left side ofregenerator 2158, thus tending to heat that warm side.

22 l Piston 2118 now strokes right, pushing hot air into the left sideof regenerator 2156 while emerging warm air from the opposite side loopspast open valve 2138 into filling region 2126 on the left of the piston.The system pressure is now low and the gas on the right side is cooledadiabatically.

22 m Piston 2120 strokes left, pushing the cooled cold volume into thecold right side of regenerator 2158, thus further cooling that side ofthe regenerator, while warm air emerges from the other side of theregenerator and loops through valve 2138 into expanding region 2104.

22 n Piston 2118 strokes left, raising pressures and temperatures.Observe that in the last few steps, pistons 2118 and 2120 have beenmoving in a quadrature sequence, one piston motion leading the other. Itis this quadrature phasing of piston motions that pumps heat. This couldbe accomplished with continuous quadrature-phase sinusoidal motions, butnon-overlapping full-stroke motions of the two pistons are moreeffective. This quadrature sequence could optionally continue forfurther cycles before the air exchange sequence to follow in thisdescription and in the figures.

22 o Piston 2120 returns to center position, pushing a half-stroke ofcompression-heated warm air into the left side of regenerator 2158.

22 p Piston 2118 strokes right, cooling the system and lowering thepressure to near-ambient.

22 q Center valve 2138 closes. All valves are now closed, and the systemhas returned to the state described with reference to FIG. 22 a. Thiscompletes the cycle.

The above examples illustrate the core principles of the invention indiffering contexts. It will be recognized that many other particularcontexts and variations are possible, falling within the teachingprovided in the above Specification and further by the following claims.

1. A heat-powered pneumatic compressor system for compressing a workingfluid from a first pressure region to a second pressure region at higherpressure than the first, comprising: a pressure containment componentconfining a volume of said working fluid in an interior region thereof;a displacer, variably dividing said interior region of said pressurecontainment component into a hot region and a cold region such thatvolume increases in one region are accompanied by volume decreases inthe other; a regenerator, disposed between said hot region and said coldregion and affecting a transient or oscillatory through-flow of saidworking fluid such that said working fluid flowing toward the hot regionis heated and said working fluid flowing toward the cold region iscooled; a heater arranged to add heat to said hot region; and valvemeans, providing controllable pneumatic coupling between said interiorregion and a pneumatic load external to said interior region, wherebyflow of said working fluid via said valve means causes a systematicone-way flow of said working fluid to or from said external pneumaticload, delivering fluid power against a pressure differential in thepneumatic load.
 2. System of claim 1 where the pneumatic load is aRankine-cycle system including a Rankine working fluid for one-way heattransfer, where the Rankine working fluid and the compressor systemworking fluid are the same.
 3. System of claim 1 where the pneumaticload is a superheated steam drying system with recycling of condensationheat and where steam from said drying system becomes the working fluid.4. System of claim 1 where the pneumatic load is a liquid distillationsystem with recycling of condensation heat, and where vapor of saiddistillation system becomes the working fluid.
 5. System of claim 1where the pneumatic load is a system for concentration of solutions bysolvent evaporation with recycling of condensation heat and where vaporfrom said solvent evaporation becomes the working fluid.
 6. Aheat-powered heat pump having a working fluid, comprising: a pressurecontainment component, confining a volume of said working fluid in aninterior region thereof, wherein the volume includes a first volume anda second volume; a first displacer, variably subdividing said interiorregion of said pressure containment component into a hot region and awarm-cold region, such that first volume increases in one such regionare accompanied by corresponding first volume decreases in another suchregion; a second displacer, variably subdividing said warm-cold regioninto a warm region and a cold region, such that second volume increasesin one such region are accompanied by corresponding second volumedecreases in another such region; a first regenerator, disposed betweensaid hot region and said warm region and affecting a transient oroscillatory through-flow of the working fluid such that the workingfluid flowing toward the hot region is heated and the working fluidflowing toward the warm region is cooled; a second regenerator, disposedbetween said warm region and said cold region and affecting a transientor oscillatory through-flow of the working fluid such that the workingfluid flowing toward the warm region is heated and the working fluidflowing toward the cold region is cooled; a heater arranged to add heatto said hot region; first valve means, providing controllable pneumaticcoupling between said warm region and a first external region; andsecond valve means, providing controllable pneumatic coupling betweensaid warm cold region and a second external region, whereby said valvemeans cause multiple periods of isolation of said interior region fromsaid first and second external regions, said multiple periodsalternating with periods of pneumatic connection between said interiorregion and said first and second external regions;
 7. System of claim 6,wherein said first and second displacers cause said subdividing volumeincreases and decreases during said multiple periods of isolation. 8.System of claim 7, wherein said volume increases and decreases caused bysaid first displacer during isolation periods induces pressure variationin said cool and cold regions, wherein said second volume increases andsecond volume decreases caused by said second displacer cause systematicone-way heat flow, responsive to said pressure variation and to saidsecond volume increases and decreases, results in unidirectional heatflow from said cold region to said warm region, lowering the temperatureof said cold region.
 9. System of claim 8, wherein said unidirectionalheat flow from said cold region raises the temperature of said warmregion, and heat flow from said hot region further raises thetemperature of said warm region, and wherein the resulting net heat flowout of said cold region and into said warm region results in heating ofsaid first external region and cooling of said second external regionduring said periods of pneumatic connection.
 10. System of claim 6,further including third valve means, providing controllable pneumaticcoupling between said heater and said hot region.
 11. System of claim10, whereby said controllable pneumatic coupling between said heater andsaid hot region provides coupling when interior region pressure is high,while said first and second valve means provide coupling when interiorregion pressure is low.
 12. A heat engine having an operating cycle forthe combined functions of pneumatic power production and waste heatremoval via flow of a working fluid, comprising: a pressure containmentcomponent, confining the volume of said working fluid in an interiorregion thereof; a displacer, variably dividing said interior of saidpressure containment into a hot region and a cold region, such thatmotion of said displacer causes volume changes in one of said regionsand opposite volume changes in the other of said regions; a regenerator,disposed between said hot region and said cold region, and affecting atransient or oscillatory through-flow of said working fluid such thatworking fluid flowing toward the hot region is heated in saidregenerator and working fluid flowing toward the cold region is cooledin said regenerator; a heater arranged to add heat to said hot region; avalve, providing intermittent pneumatic coupling periods between one ofsaid hot region and said cold region and a pneumatic load external tosaid interior region when said valve is open, and providing intermittentdecoupling periods between said region and said load when said valve isclosed; wherein said displacer motion causes pressure change in saidinterior region during said decoupling periods and causes volumedisplacement with energy transfer during said coupling periods.
 13. Theheat engine of claim 12 wherein said energy transfer includes transferof pneumatic energy as the product of pressure difference times volumedisplacement and further includes transfer of waste heat energy out ofsaid heat engine.
 14. The heat engine of claim 13 wherein said pneumaticenergy transfer performs pneumatic output work on a coupled system. 15.The heat engine of claim 14 wherein said coupled system is a RankineCycle heat pump, wherein said pneumatic output work drives said heatpump, and wherein said heat pump operates with the same working fluid assaid heat engine.
 16. The heat engine of claim 14, wherein said coupledsystem is a Stirling-like vapor-phase heat pump, wherein said heat pumpshares the same working fluid as said heat engine, and wherein said heatpump includes a second regenerator and a second displacer and operatessaid second displacer in coordination with said pneumatic energytransfer to transform said pneumatic energy into separate output streamsof said working fluid, one of said streams being colder than acorresponding input stream of working fluid due to heat pumping intoanother one of said separate output streams.
 17. A heat engine having anoperating cycle for the combined functions of pneumatic power productionand waste heat removal via flow of a working fluid, comprising: apressure containment component, intermittently confining the volume ofsaid working fluid in an interior region thereof; a regenerator,disposed between a hot region and a cooler region of said interiorregion, and affecting a transient or oscillatory through-flow of saidworking fluid such that said working fluid flowing toward the hot regionis heated in said regenerator and said working fluid flowing toward thecooler region is cooled in said regenerator; a displacer, variablydividing said interior of said pressure containment into said hot regionand said cooler region, such that motion of said displacer causes volumechanges in one of said regions and opposite volume changes in the otherof said regions, thereby causing said transient or oscillatorythrough-flow in said regenerator; a heater arranged to add heat to saidhot region; a valve, providing intermittent periods of coupling of saidworking fluid to a region external to said interior region when saidvalve is open, and providing intermittent periods of decoupling betweensaid interior region and said external region when said valve is closed;wherein said displacer motion causes pressure change in said interiorregion during said decoupling periods and causes volume displacementwith energy transfer between said external and interior regions duringsaid coupling periods, wherein said energy transfer during said couplingperiods includes the transfer of waste heat energy for said heatremoval, and, wherein said heat engine causes pneumatic energy transfer,as the product of pressure change and volume displacement, said energytransfer causing heat to be pumped against a temperature gradient. 18.The heat engine of claim 17, wherein said region external to saidinterior region includes a Rankine Cycle, wherein said pneumatic energytransfer drives said Rankine Cycle, and wherein said Rankine Cycleoperates with the same working fluid as said heat engine.
 19. The heatengine of claim 18, wherein said Rankine Cycle is a closed refrigerantcycle sharing the same working fluid as said heat engine, and whereinsaid Rankine cycle pumps heat by causing condensation of said workingfluid at an elevated pressure in a condenser and evaporation of saidworking fluid at a lower pressure in an evaporator.
 20. The heat engineof claim 18, wherein said Rankine Cycle is an open cycle for theevaporative removal of said working fluid from a material, wherein atleast part of said working fluid removed from said material iscompressed by said heat engine and caused to condense, wherebycondensation heat promotes more of said evaporative removal.
 21. Theheat engine of claim 20, wherein said working fluid caused to condenseis collected as a purified distillate.
 22. The heat engine of claim 20,wherein said material is a liquid solution and wherein said evaporativeremoval from said material causes said solution to be concentrated. 23.The heat engine of claim 20, wherein said material is a solid materialwetted by the liquid phase of said working fluid and wherein saidevaporative removal from said material causes said material to be dried.24. The heat engine of claim 17 further including a coupledStirling-like vapor-phase heat pump, said heat pump being pneumaticallycoupled to said heat engine, said heat pump including a secondregenerator and a second displacer, operated cyclically in coordinationwith operation of said heat engine, wherein said pneumatic energy fromsaid heat engine causes compression and expansion of said working fluidin said heat pump, wherein said compression and expansion causes cyclictemperature change in said working fluid in said heat pump, and whereinsaid cyclic temperature change varies in-phase with volume displacementof said second displacer, thereby causing compression-heated workingfluid to flow systematically into a first end of said second regeneratorand expansion-cooled working fluid to flow systematically into anopposing second end of said second regenerator.
 25. The heat engine ofclaim 24, wherein said compression-heated and expansion-cooled flows ofsaid working fluid in said heat pump occur, at least in part, when saidvalve is closed to augment pressure change, wherein working fluidintermittently flows into said heat pump from part of said externalregion during at least some of said intermittent periods of couplingwhen said valve is open, and wherein cooled working fluid intermittentlyflows out of said heat pump into a different part of said externalregion during at least some of said intermittent periods of couplingwhen said valve is open, whereby heat is pumped from said working fluidthat flows into said heat pump to produce said cooled working fluid thatflows out of said heat pump.
 26. The heat engine of claim 24, operatedto cool a space.
 27. The heat engine of claim 24, operated to heat aspace with a combination of pumped heat and said waste heat from theoperation of said heat engine and from energy losses in said heat pump.28. A heat engine providing combined pneumatic power output and pistonpower output with convective cooling of an internal regenerator,comprising: a pressure containment component, intermittently confiningthe volume of a working fluid in an interior region thereof; aregenerator, disposed between a hot region and a cooler region of saidinterior region, and affecting a transient or oscillatory through-flowof said working fluid such that said working fluid flowing toward thehot region is heated in said regenerator and said working fluid flowingtoward the cooler region is cooled in said regenerator; a displacer,variably dividing said interior of said pressure containment into saidhot region and said cooler region, such that motion of said displacercauses volume changes in one of said regions and opposite volume changesin the other of said regions, thereby causing said transient oroscillatory through-flow in said regenerator and further causingpressure variation, volume displacement, and output work through theheating and cooling action of said regenerator; a heater arranged to addheat to said hot region; one or more valves, providing intermittentperiods of coupling of said working fluid to a region external to saidinterior region when said one or more of said one or more valves areopen, and providing intermittent periods of decoupling between saidregion and said load when one or more of said one or more valves areclosed; a piston having two working areas, a first area operatingbetween said interior region and said external region, and a largersecond area functioning as said displacer within said interior region; amotor/generator, coupled to said piston, initiating and powering themotion of said piston as needed, and receiving power from said piston togenerate electricity under specific pneumatic loading conditions; apneumatic load, receiving pneumatic power via said one or more valvesand causing said specific pneumatic loading conditions; whereby couplingof working fluid flow to said pneumatic load via said valves causesconvective cooling of said cooler region; and, whereby said couplingcauses said specific pneumatic loading conditions, which include a phaseshift in said pressure variation relative to the displacement phase ofsaid piston, thereby causing a shift from reactive pressure phase topower-generating pressure phase in the oscillatory pressure exerted onsaid first area of said piston, resulting in power generation.